2011 Particle Accelerator Conference - Classification: Advanced Concepts and Future Directions / Tech 01: Proton and Ion Sources

Paper	Title	Page
MOP153	High Efficiency Laser Ion Acceleration in Low Density Plasmas	376
	E. d'Humières, V. Tikhonchuk CELIA, Talence, France
	Laser driven sources of high energy ions commonly use thin solid foils. A gaseous target can also produce ion beams with characteristics comparable to those obtained with solid targets. Using Particle-In-Cell simulations, we have studied in detail ion acceleration with high intensity laser pulses interacting with low density plasmas. A two-step acceleration process can be triggered: first, ions are accelerated in volume by electric fields generated by hot electrons, second, the ion energy is boosted in a strong electrostatic shock. 2D and 3D simulations show the potential of this regime. It is possible to model separately these two steps. In the first step a hot electron population and a descending density profile are necessary, and the second step develops if a fast proton wave enters in a low density plasma.

MOP154	Prospects for Proton Accelerators Driven by the Radiation Pressure from a Sub-PW CO2 Laser	379
	M.N. Polyanskiy, I. Ben-Zvi, I. Pogorelsky, V. Yakimenko BNL, Upton, Long Island, New York, USA Z. Najmudin Imperial College of Science and Technology, Department of Physics, London, United Kingdom
	Funding: DOE Laser acceleration of ion beams is normally realized via irradiating thin-foil targets with near-IR solid-state lasers with up to petawatt (PW) peak power. Despite demonstration of significant achievements, further progress towards practical application of such beam sources is hindered by the challenges inherent in constructing still more intense and higher-contrast lasers. Our recent studies of the radiation pressure acceleration indicate that the combination of a 10-μm CO2 laser with a gas jet target offers a unique opportunity for a breakthrough in the field. Strong power scaling of this regime holds the promise of achieving the hundreds of MeV proton beams with just sub-PW CO2 laser pulses. Generation of such pulses is a challenging task. We discuss a strategy of the CO2 laser upgrade aimed to providing a more compact and economical hadron source for cancer therapy. This include optimization of the method of the 10μm short-pulse generation, higher amplification in the CO2 gas under combined isotopic and power broadening effects, and the pulse shortening to a few laser cycles (150-200 fs) via self-chirping in the laser-produced plasma and the consecutive dispersive compression.

TUOBN6	Production of 25 MeV Protons in CO2 Laser-Plasma Interactions in a Gas Jet	721
	D.J. Haberberger, C. Gong, C. Joshi, S. Tochitsky UCLA, Los Angeles, California, USA
	Funding: This work is supported by DOE grant DE-FG02-92ER40727 and NSF grant PHY-0936266 At the Neptune Laboratory at UCLA, we have developed a high-power CO2 MOPA laser system which produces world record multi-terawatt 10um pulses. The CO2 laser pulses consist of a train of 3ps pulses separated by 18ps, each with a peak power of up to 4TW and a total pulse train energy of ~100J. These relativistic laser pulses are applied for Laser Driven Ion Acceleration in an H2 gas jet operated around the critical density of 10¹⁹ cm^-3 for 10um light using the Target Normal Sheath Acceleration mechanism. The laser is focused into the gas jet reaching a normalized field strength of a₀~2 in vacuum. For these conditions, protons with a maximum energy of 25MeV and a narrow energy spread of ΔE/E < 1% are recorded. Initial analysis of these experimental results shows a stronger scaling of the proton energy than that predicted from the ponderomotive force, and highlights the importance of an accumulated effect of multiple CO₂ laser pulses lasting over 100ps. The temporal dynamics of the overdense plasma slab are probed with a picosecond 532nm pulse and the results will be discussed.

Paper

Title

Page

High Efficiency Laser Ion Acceleration in Low Density Plasmas

376

E. d'Humières, V. Tikhonchuk
CELIA, Talence, France

Laser driven sources of high energy ions commonly use thin solid foils. A gaseous target can also produce ion beams with characteristics comparable to those obtained with solid targets. Using Particle-In-Cell simulations, we have studied in detail ion acceleration with high intensity laser pulses interacting with low density plasmas. A two-step acceleration process can be triggered: first, ions are accelerated in volume by electric fields generated by hot electrons, second, the ion energy is boosted in a strong electrostatic shock. 2D and 3D simulations show the potential of this regime. It is possible to model separately these two steps. In the first step a hot electron population and a descending density profile are necessary, and the second step develops if a fast proton wave enters in a low density plasma.

MOP154

Prospects for Proton Accelerators Driven by the Radiation Pressure from a Sub-PW CO2 Laser

379

M.N. Polyanskiy, I. Ben-Zvi, I. Pogorelsky, V. Yakimenko
BNL, Upton, Long Island, New York, USA
Z. Najmudin
Imperial College of Science and Technology, Department of Physics, London, United Kingdom

Funding: DOE
Laser acceleration of ion beams is normally realized via irradiating thin-foil targets with near-IR solid-state lasers with up to petawatt (PW) peak power. Despite demonstration of significant achievements, further progress towards practical application of such beam sources is hindered by the challenges inherent in constructing still more intense and higher-contrast lasers. Our recent studies of the radiation pressure acceleration indicate that the combination of a 10-μm CO2 laser with a gas jet target offers a unique opportunity for a breakthrough in the field. Strong power scaling of this regime holds the promise of achieving the hundreds of MeV proton beams with just sub-PW CO2 laser pulses. Generation of such pulses is a challenging task. We discuss a strategy of the CO2 laser upgrade aimed to providing a more compact and economical hadron source for cancer therapy. This include optimization of the method of the 10μm short-pulse generation, higher amplification in the CO2 gas under combined isotopic and power broadening effects, and the pulse shortening to a few laser cycles (150-200 fs) via self-chirping in the laser-produced plasma and the consecutive dispersive compression.

TUOBN6

Production of 25 MeV Protons in CO2 Laser-Plasma Interactions in a Gas Jet

721

D.J. Haberberger, C. Gong, C. Joshi, S. Tochitsky
UCLA, Los Angeles, California, USA

Funding: This work is supported by DOE grant DE-FG02-92ER40727 and NSF grant PHY-0936266
At the Neptune Laboratory at UCLA, we have developed a high-power CO2 MOPA laser system which produces world record multi-terawatt 10um pulses. The CO2 laser pulses consist of a train of 3ps pulses separated by 18ps, each with a peak power of up to 4TW and a total pulse train energy of ~100J. These relativistic laser pulses are applied for Laser Driven Ion Acceleration in an H2 gas jet operated around the critical density of 10¹⁹ cm^-3 for 10um light using the Target Normal Sheath Acceleration mechanism. The laser is focused into the gas jet reaching a normalized field strength of a₀~2 in vacuum. For these conditions, protons with a maximum energy of 25MeV and a narrow energy spread of ΔE/E < 1% are recorded. Initial analysis of these experimental results shows a stronger scaling of the proton energy than that predicted from the ponderomotive force, and highlights the importance of an accumulated effect of multiple CO₂ laser pulses lasting over 100ps. The temporal dynamics of the overdense plasma slab are probed with a picosecond 532nm pulse and the results will be discussed.